Interpretation of the Methylene Blue Reduction Test of Human Plasma and the Possible Cancer Protecting Effect of Selenium: The time required for the reduction of a given amount of methylene blue (MB) by human plasma has previously been found to be longer in samples taken from cancer patients. The MB reduction time has now been found to be mainly determined by the amount of selenium present in plasma. Cancer patients in turn are often low in plasma Se. The human cancer mortality in the U.S. accordingly depends on the dietary selenium intake and is the highest in selenium deficient areas. The Vitamin E and Selenium Status of Infants and the Sudden Infant Death Syndrome: D. F. L. Money suggested vitamin E and/or selenium deficiency as a possible cause of the Sudden Infant Death Syndrome (SIDS) on the basis of observations with animals. We have tested his hypothesis by comparing vitamin E and Se blood or plasma levels of SID samples with those of normal controls. Initial results indicate that vitamin E and Se levels of SID cases are similar to those of normal controls. First communication on the subject was published. A more detailed statistical and experimental study is underway.